In a knitting machine such as a circular knitting machine or flat knitting machine, the vertical movement of working needles is selected on the basis of a knitting procedure stored in a storage such as a floppy disk to form a fabric having a desired knitting texture. Various types of needle selectors are used to select the vertical movement of the working needles.
A needle selector of this type will be described. First, the outline of needle selecting operation in a knitting machine will be described through a circular knitting machine schematically shown in FIGS. 14, 15A, and 15B.
FIG. 14 is a schematic perspective view for explaining the basic knitting mechanism of a circular knitting machine. As shown in FIG. 14, in the circular knitting machine, working needles 52 are slidably arranged in a plurality of vertical grooves (not shown) formed along the longitudinal axis in the outer surface of a knitting cylinder 51 which rotates as indicated by an arrow A. As shown in FIGS. 15A and 15B, needle selection jacks 53 are arranged under the working needles 52 to be able to abut against the lower portions of the working needles 52. A cylindrical cam base 54a is set still under the knitting cylinder 51. A plurality of cams 54 each having a predetermined shape are arranged above the cam base 54a at a predetermined interval. The cams 54 push up the needle selection jacks 53 to push the working needles 52 upward.
The basic knitting principle is as follows. When a working needle 52 on the rotating knitting cylinder 51 is pushed upward through the needle selection jack 53, the working needle 52 projects from the upper surface of the knitting cylinder 51. A yarn 56 taken out from a yarn bobbin 55 is supplied to the hook of the projecting working needle 52 to form a yarn loop. Subsequently, the working needle 52 is moved downward by a known mechanism (not shown) to form one stitch. By selecting whether or not a vertical movement is to be applied to the working needle 52, a stitch may be formed, or may not be formed but the process advances to the next knitting step, thus forming a desired fabric. In order to actuate the working needles in this manner, in the knitting machine, generally, the needle selection jacks 53 are arranged under the working needles 52 to abut against the working needles 52. The needle selection jacks 53 are selectively engaged with the working needles 52 by using a needle selector 57, which operates on the basis of information from a controller 58 incorporating a storage that stores a knitting procedure for a knitting texture, to control the vertical movement of the working needles 52.
A case wherein a piezoelectric body is used as a needle selecting means will be described hereinafter with reference to FIGS. 15A and 15B which show the relationship among the working needle, selection jack, and needle selecting means.
A piezoelectric body 2 can be bent as shown in FIG. 15A or bent as shown in FIG. 15B in a direction opposite to that in FIG. 15A depending on how a voltage is applied to the piezoelectric body 2. A finger 5 is arranged to be connected to the front end of the piezoelectric body 2. The piezoelectric body 2, finger 5, and cam 54 are positioned as shown FIGS. 15A and 15B. The working needle 52 and needle selection jack 53 move circularly together with the knitting cylinder 51 (not shown) downward from the front side of the sheet of drawing to the back side of the sheet (or in the opposite direction). The needle selection jack 53 can swing about a fulcrum 53a as the center. A needle selection butt 69 and cam butt 70 are arranged so as to project from the needle selection jack 53 sideways as shown in FIGS. 15A and 15B.
When the piezoelectric body 2 is bent as shown in FIG. 15A, the needle selection butt 69 of the needle selection jack 53 which moves circularly collides against the finger 5. Consequently, the cam butt 70 of the needle selection jack 53 cannot engage with the cam 54. Hence, the needle selection jack 53 is not pushed upward by the cam 54, and the working needle 52 is not pushed upward.
When the piezoelectric body 2 is bent as shown in FIG. 15B, the finger 5 at the front end of the piezoelectric body 2 does not collide against the needle selection butt 69 of the needle selection jack 53 which moves circularly together with the knitting cylinder 51, and the needle selection jack 53 maintains the vertical posture. Consequently, the cam butt 70 at the lower end of the needle selection jack 53 is pushed upward along the inclined surface of the cam 54, and accordingly the working needle 52 is pushed upward.
When the needle selection butt 69 of the needle selection jack 53 and the finger 5 at the front end of the piezoelectric body 2 are engaged selectively in this manner, the working needle 52 can be moved upward freely as required, and a fabric having an arbitrary knitting texture can be knitted.
The most significant performance in knitting is high productivity, in other words, the capability of increasing the rotational speed of the knitting cylinder. To increase the rotational speed of the knitting cylinder 51, the needle selector 57 which controls the upward movement of the working needles 52 must be operated at a high speed. For this purpose, various types of needle selectors for knitting which operate at a high speed have been developed and used.
For example, the applicant of the present invention proposed a needle selector (see Japanese Patent Laid-Open No. 60-224845) in which the attraction or repulsion force of an electromagnet is used to enable a plurality of fingers to swing. This needle selector has a higher operation speed and smaller size than the conventional needle selector, thus achieving reduction of the power consumption. The applicant of the present invention also proposed a piezoelectric needle selector (see Japanese Patent Laid-Open No. 62-28451) to replace the needle selector using the electromagnet described above. According to this needle selector, the finger is actuated by bending a piezoelectric body to select a working needle. A higher operation speed, smaller size, and lower energy of the needle selector were achieved.
The applicant of the present invention also invented an improved apparatus of the piezoelectric needle selector described above, and filed it on Oct. 5, 1988, as Japanese Patent Application No. 63-249967 with the title “Needle Selector for Knitting Machine”. This invention is registered as Japanese Patent No. 1969970 (see Japanese Patent Publication No. 6-94619), and its counterpart U.S. patent application is registered as U.S. Pat. No. 5,027,619.
FIG. 12A shows the piezoelectric needle selector described in Japanese Patent No. 1969970. As shown in FIG. 12A, according to the improved needle selector, a finger 5 is rotatably arranged on a piezoelectric body 2 having a piezoelectric element. Power is applied to the piezoelectric element to actuate the finger 5. A working needle of a knitting machine is selected by operation of the finger 5 (more particularly, through a jack) so that a fabric having a desired pattern texture can be knitted. According to the characteristic feature of this needle selector, the rear end portion of the piezoelectric body 2 is rotatably supported by a support A or housing through a rotary member 1A. The front end portion of the piezoelectric body 2 is rotatably connected to a U-shaped groove in the rear end portion of the finger 5 through a rotary member 1B. An intermediate position between the rear end portion and front end portion of the piezoelectric body 2 is clamped by rotary members 30 rotatably provided to a support body 13 or the housing. The finger 5 and piezoelectric body 2 are disposed on one straight line.
As shown in FIG. 12A, the intermediate portion of the piezoelectric body 2 is supported by the support body 13 through the rotary members 30. When the piezoelectric body 2 bends, it vertically moves a rear end 5A of the finger 5. The vertical movement of the rear end 5A vertically moves a front end 5B of the finger 5 which projects through an opening 19a of a support body 19. Consequently, the upward movement of a working needle 52 is selected.
The present applicant found that when the piezoelectric body 2 is rotatably supported at its predetermined position in this manner, the piezoelectric body 2 can bend freely. As a result, the moving speed of the finger 5 increases greatly and the moving amount of the front end of the finger 5 increases. When the piezoelectric body is used with this structure, damage to the piezoelectric body is decreased to prolong the service life of the needle selector. In this improved piezoelectric needle selector, as the structure of the finger actuating device which swings the finger member is improved greatly, the needle selecting ability is improved remarkably.
Basically, a piezoelectric body vibrates in all directions (360°) in a plane when power is applied to it. This is understandable from the fact that the piezoelectric body is originally introduced as a loudspeaker vibrating plate. When the piezoelectric body which vibrates in all directions is formed into a rectangular plate and one end of the long side of the plate is fixed, the plate forms a cantilevered beam the other end of which swings vertically. Even in this case, as the piezoelectric body vibrates in all directions, a vibration component in the widthwise direction of the rectangular piezoelectric body remains. Conventionally, a person skilled in the art overlooks this vibration component generated in the widthwise direction as inevitable.
In the conventional needle selector shown in FIG. 12A, the rotary member 30 which holds the piezoelectric body 2 at the intermediate position is a cylindrical member having a slit 32 extending from the end face of the rotary member 30 in the direction of longitudinal axis to hold the piezoelectric body 2, as shown in the detailed view of FIG. 12B. A shaft neck 31a at the end portion of the rotary member 30 and having a circular section is inserted in a circular hole (not shown) formed in the support body 13, so that the rotary member 30 is supported rotatably.
In the example shown in FIG. 12A, the rotary members 30 clamp the piezoelectric body 2 by the slits 32 from the left and right. Alternatively, as shown in FIG. 13, one cylinder 40 having a slit (not shown) at its central portion to clamp a piezoelectric body 2 may be used.
In this case as well, shaft necks 40a and 40b each having a circular section are inserted and held in the circular holes of the support body 13, so that the piezoelectric body 2 is supported rotatably.
In the conventional needle selector, as described above with reference to FIGS. 12B and 13, the cylinder that rotatably holds the piezoelectric body at the intermediate position is a cylindrical member having a circular section.
As described above, while the present inventors concentrate on an increase in operation speed, downsizing, and energy saving of a needle selector for a knitting machine and take various types of measures for these purposes to make results, a higher performance has yet been required.
In view of this, the present inventors have made extensive studies to obtain a more efficient swing movement with a piezoelectric body, and reached the following conclusion. Namely, as far as a cylindrical member having a circular section is used, it is difficult to let the vibration of a piezoelectric body focus in the longitudinal direction more efficiently. In particular, when the needle selector is further downsized, the diameter of the cylinder which rotatably holds the piezoelectric body at the intermediate position tends to decrease. The present inventors found that the smaller the diameter of the cylinder, the more apparently vibration tends to occur in the widthwise direction.
It is an object of the present invention to provide a needle selector having a novel structure for a knitting machine, which can suppress as much as possible a loss in swing movement of a piezoelectric body of a conventional needle selector for a knitting machine.